There is a strong need in the industry to provide effective stripping of a variety of cured paints and powder coatings from substrates, such as steel, aluminium, galvanized steel, magnesium, engineering plastics etc. for the re-working of a part which has a flawed coating or for reclaiming parts in which the substrate is intact but which requires residues to be removed and/or new coatings to be applied. In addition to the removal of organic coatings or residues from a substrate residues such as greases, oils, mold-release coatings, polyester coatings, epoxy coatings, paints and other types of coatings, is desired.
US 2005/0079984 A1 teaches a method to strip cured paint from various substrate materials. The composition of this invention consists of a mixture of, not limited to, two surfactants selected from the group consisting; a) surfactants, non-ionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, acetate based surfactants, acetylene based, fluorosurfactants, solvent based surfactants, phosphate ester surfactants, acid pH based surfactants, alkaline pH based surfactants, neutral pH surfactants, sulfonic acid surfactants, phosphoric acid surfactants, fatty acid based surfactants, inorganic acid based surfactants, carboxylate based surfactants, alkylate based surfactants, alcohol based surfactants, nonylphenol surfactants, oxide-based surfactants, sulfur based surfactants, alkylphenol containing surfactants, ethoxylated surfactants, sulphonated surfactants, amine based surfactants, amide surfactants, glycol based surfactants and quaternary surfactants and surfactant blends thereof, comprising 51% to 100% of the total weight or volume of the composition, with the remaining 0.5%-49% balance consisting of additives selected by the group consisting; water, organic solvents, alcohols, aliphatic solvents, polar solvents, non-polar solvents, naphtha, oxygenated solvents, chlorinated solvents, acetones, ketones, acetates, terpene solvents, esters, acetylene solvents, glycols, ethers, propionate solvents, carbonates, aromatic solvents, kerosene, fatty acid based solvents, vegetable based solvents, acids, inorganic acids, organic acids, fatty acids, lactic acids, glycolic acids, alkaline hydroxides, alkaline silicates, phosphates, sulfates, nitrates, alkaline salts, acid salts, ethanol amines, peroxides, oxidizers, rust inhibitors, chelators, defoamers, surfactants and mixtures thereof; b) immersing said cured painted substrate in said strip tank containing said stripping composition; and c) heating said stripping composition from 65 to 180° C. for approximately 1-3 hours, wherein cured paint is removed from said substrate.
It is known that caustic compounds used at elevated temperatures in an essentially anhydrous condition are very effective in removing many types of organic coatings and residues from many types of metal substrates. One such method is taught by U.S. Pat. No. 3,790,489. However, certain metals, such as zinc, aluminum and magnesium or metallic coatings comprised of these metals or alloys thereof, as well as other metals, alloys, and even non-metallic substrates, are subject to chemical attack or destruction under such conditions as taught in the '489 patent. Thus, such caustic compositions are typically avoided in prior art teachings when removing coatings from metals, such as aluminum, magnesium and zinc.
A prior art method which avoids the use of a caustic solution is taught by U.S. Pat. No. 5,894,854. The invention relates to a method of stripping cured paint from a non-ferrous substrate comprising: a) adding a stripping composition to a strip tank, said stripping composition consisting an alkylphenol-hydroxypoly-oxyethlene and triethanolamine; b) immersing said nonferrous substrate in said strip tank containing said stripping composition; and c) heating said stripping composition to 180° C. for approximately 60 minutes, wherein cured paint is removed from said non-ferrous substrate
In U.S. Pat. No. 3,954,648 is disclosed a solution with a high boiling liquid amine, and an alkali metal hydroxide. Belcak et al also suggest the use of a surface active wetting agent if needed.
U.S. Pat. No. 6,855,210 relates to a composition and method for stripping and cleaning organic coatings from substrates, comprising a solution of high-boiling alcohols, preferably polyglycols, a surfactant, preferably a nonylphenol ethoxylate, and an alkali metal hydroxide. The composition aggressively and effectively strips paints and other organic coatings without harming underlying substrates damaged by prior art strippers, over conventional or lower time periods, and at conventional or lower temperatures. One embodiment of the invention comprises from about 40% to about 98.9% by weight of a high-boiling alcohol; from about 1% to about 60% of a non-ionic surfactant; and from about 0.1% to about 10% of an alkali hydroxide or mixture of alkali hydroxides. A preferred surfactant used is based on hazardous nonylphenol ethoxylate.
The measurement was performed on a SIGMA VP Field Emission Scanning Electron Microscope from Carl Zeiss at 1000× magnification and at a low accelerating voltage (3 kV).